Body waves, including P and S waves, travel through solids, liquids, and gases. P waves are faster compressional waves, while S waves are slower shear waves that only travel through solids. Surface waves like R and L waves travel along or below the surface. The difference in arrival times of seismic waves at multiple seismograph stations can be used to locate an earthquake's epicenter by drawing circles around each station. Both the intensity of ground shaking and magnitude, measured on the Richter scale, are used to measure an earthquake's size and strength, with magnitude being independent of intensity. Earthquakes can cause ground shaking and damage that increases in poorly consolidated rock. While some monitoring and studies aim to predict or control qu

10. •Body waves
•P or primary waves
•fastest waves
•travel through solids, liquids, or
gases
•compressional wave, material
movement is in the same direction
as wave movement
•S or secondary waves
•slower than P waves
•travel through solids only
•shear waves - move material
perpendicular to wave movement

11. Surface Waves: R and L waves
Surface Waves
Travel just below or along the ground’s
surface
Slower than body waves; rolling and side-to-
side movement
Especially damaging to buildings

12. How is an Earthquake’s Epicenter Located?
 Seismic wave behavior
P waves arrive first, then S waves, then L and R
Average speeds for all these waves is known
After an earthquake, the difference in arrival times at
a seismograph station can be used to calculate the
distance from the seismograph to the epicenter.

13. How is an Earthquake’s Epicenter Located?
Time-distance
graph showing the
average travel
times for P- and S-
waves. The farther
away a
seismograph is
from the focus of
an earthquake, the
longer the interval
between the
arrivals of the P-
and S- waves

14. How is an Earthquake’s Epicenter Located?
•Three seismograph
stations are needed to
locate the epicenter of an
earthquake
•A circle where the radius
equals the distance to the
epicenter is drawn
•The intersection of the
circles locates the
epicenter

15. How are the Size and Strength of an Earthquake Measured?
•Intensity
1. subjective measure of
the kind of damage
done and people’s
reactions to it
2. isoseismal lines
identify areas of equal
intensity
• Modified Mercalli Intensity Map
– 1994 Northridge, CA
earthquake, magnitude 6.7

16. How are the Size and Strength of an Earthquake Measured?
•Magnitude
1. Richter scale
measures total
amount of energy
released by an
earthquake;
independent of
intensity
2. Amplitude of the
largest wave
produced by an
event is corrected
for distance and
assigned a value
on an open-ended
logarithmic scale

17. What are the Destructive Effects of Earthquakes?
•Ground Shaking
amplitude, duration, and damage
increases in poorly consolidated rocks

18. Can Earthquakes be Predicted?
Earthquake Precursors
―changes in elevation or tilting of land
surface, fluctuations in groundwater levels,
magnetic field, electrical resistance of the
ground
―seismic dilatancy model
―seismic gaps

19. Can Earthquakes be Predicted?
Earthquake Prediction Programs
―include laboratory and field studies of rocks
before, during, and after earthquakes
―monitor activity along major faults
―produce risk assessments

20. Can Earthquakes be Controlled?
•Graph showing the relationship between the
amount of waste injected into wells per
month and the average number of Denver
earthquakes per month
•Some have suggested that pumping fluids
into seismic gaps will cause small
earthquakes while preventing large ones

21. Name:A.YodhaGopaal.
Class: IX (C.B.S.E)